A processing step can typically generate a result on the basis of a set of results of certain preceding processing steps. For example, a processing step numbered K may comprise the calculation of a result on the basis of the results of the last three preceding processing steps: the steps numbered K-1, K-2 and K-3, K being an integer greater than 3. Each processing step in such a data processing operation provides a new result. Indeed, it is as though there is a basket of results, which is gradually filled by carrying out the processing steps. In each processing step another result is added to certain results which are assumed to be already in the basket. This is a process of gradual growth. An example of such data processing is the contextual arithmetic decoding in accordance with the MPEG4 standard.